Define Extra Class For Compound Key : Primary Key « JPA « Java Tutorial

1. Java Tutorial
2. JPA
3. Primary Key

File: Employee.java

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;

@Entity
@IdClass(EmployeePK.class)
public class Employee implements java.io.Serializable {
  private String firstName;
  @Id
  private String lastName;

  @Id
  private long ssn;

  public String getFirstName() {
    return firstName;
  }

  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }


  public String getLastName() {
    return lastName;
  }

  public void setLastName(String lastName) {
    this.lastName = lastName;
  }

  public long getSsn() {
    return ssn;
  }

  public void setSsn(long ssn) {
    this.ssn = ssn;
  }
}

class EmployeePK implements java.io.Serializable {
  private String lastName;

  private long ssn;

  public EmployeePK() {
  }

  public EmployeePK(String lastName, long ssn) {
    this.lastName = lastName;
    this.ssn = ssn;
  }

  public String getLastName() {
    return this.lastName;
  }

  public void setLastName(String lastName) {
    this.lastName = lastName;
  }

  public long getSsn() {
    return ssn;
  }

  public void setSsn(long ssn) {
    this.ssn = ssn;
  }

  public boolean equals(Object obj) {
    if (obj == this)
      return true;
    if (!(obj instanceof EmployeePK))
      return false;
    EmployeePK pk = (EmployeePK) obj;
    if (!lastName.equals(pk.lastName))
      return false;
    if (ssn != pk.ssn)
      return false;
    return true;
  }

  public int hashCode() {
    return lastName.hashCode() + (int) ssn;
  }
}

File: Helper.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class Helper {
  public static void checkData() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    Connection conn = DriverManager.getConnection("jdbc:hsqldb:data/tutorial", "sa", "");
    Statement st = conn.createStatement();

    ResultSet mrs = conn.getMetaData().getTables(null, null, null, new String[] { "TABLE" });
    while (mrs.next()) {
      String tableName = mrs.getString(3);
      System.out.println("\n\n\n\nTable Name: "+ tableName);

      ResultSet rs = st.executeQuery("select * from " + tableName);
      ResultSetMetaData metadata = rs.getMetaData();
      while (rs.next()) {
        System.out.println(" Row:");
        for (int i = 0; i < metadata.getColumnCount(); i++) {
          System.out.println("    Column Name: "+ metadata.getColumnLabel(i + 1)+ ",  ");
          System.out.println("    Column Type: "+ metadata.getColumnTypeName(i + 1)+ ":  ");
          Object value = rs.getObject(i + 1);
          System.out.println("    Column Value: "+value+"\n");
        }
      }
    }
  }
}

File: Main.java

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

public class Main {
  static EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAService");

  static EntityManager em = emf.createEntityManager();

  public static void main(String[] a) throws Exception {
    em.getTransaction().begin();




    em.getTransaction().commit();
    em.close();
    emf.close();

    Helper.checkData();
  }
}

File: persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
  <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
      <property name="hibernate.connection.username" value="sa"/>
      <property name="hibernate.connection.password" value=""/>
      <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
  </persistence-unit>
</persistence>

22.19.Primary Key
	22.19.1.	Use UUID As Primary Key
	22.19.2.	Use Current Milisecond As ID
	22.19.3.	Set Primary Key Join Column For Entities In Hierarchy
	22.19.4.	Set ID By Yourself
	22.19.5.	Not Nullable ID
	22.19.6.	ID Entity With Hash Code And Equals
	22.19.7.	Id Containing Relationship
	22.19.8.	Embedded Compound Primary Key
	22.19.9.	Define Extra Class For Compound Key